Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.53   5.372%   $97.5007   $97.50   $97.50   $97.50  
  Purchase #2 $49.45   8.768%   $53.7858   $53.79   $53.80   $53.80  
  Purchase #3 $158.48   9.290%   $173.2028   $173.20   $173.20   $173.20  
  Purchase #4 $197.48   4.259%   $205.8907   $205.89   $205.90   $205.90  
  Purchase #5 $140.58   9.317%   $153.6778   $153.68   $153.70   $153.70  
  Purchase #6 $181.49   5.868%   $192.1398   $192.14   $192.15   $192.10  
  Purchase #7 $171.44   8.332%   $185.7244   $185.72   $185.70   $185.70  
  7 purchase totals = $991.45       $1,061.9220   $1,061.92   $1,061.95   $1,061.90